Method for Producing a Light-Emitting Diode

ABSTRACT

A method is provided for producing a light-emitting diode. In one embodiment, a series of layers is deposited on the silicon surface of a carrier in a direction of growth and a light-emitting diode structure is deposited on the series of layers. The series of layers includes a GaN layer, which is formed with gallium nitride. The series of layers includes a masking layer, which is formed with silicon nitride. The masking layer follows at least part of the GaN layer in the direction of growth.

This is a continuation application of U.S. application Ser. No.13/499,232, entitled “Method for Producing a Light-Emitting Diode” whichwas filed on May 11, 2012 and is a national phase filing under section371 of PCT/EP2010/064353, filed Sep. 28, 2010, which claims the priorityof German patent application 10 2009 047 881.7, filed Sep. 30, 2009, allof which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

A method for producing a light-emitting diode is specified.

BACKGROUND

The documents WO 2007/096405 (U.S. counterpart application publication2007/0197004) and U.S. Pat. No. 6,611,002 describe epitaxiallydepositing gallium nitride-based layers on a silicon substrate.

SUMMARY OF THE INVENTION

In one aspect, the present invention specifies a method by which galliumnitride-based layers having a high layer thickness and high materialquality can be deposited on a silicon surface.

In accordance with at least one embodiment of the method for producing alight-emitting diode, one method step involves providing a carriersubstrate having a silicon surface. For this purpose, the carriersubstrate can comprise silicon, for example. Furthermore, it is possiblefor the carrier substrate to be an SOI substrate (Silicon-On-InsulatorSubstrate). The silicon surface of the carrier substrate is a (111)silicon surface, for example.

The carrier substrate is distinguished, for example, by its good thermalconductivity of at least 130 W/(mK).

In accordance with at least one embodiment of the method, one methodstep involves depositing a layer sequence on the silicon surface. By wayof example, the layer sequence is applied epitaxially to the siliconsurface. The layer sequence has a growth direction in which it is grownonto the silicon surface. By way of example, the growth direction isperpendicular to the silicon surface or forms a small angle of <7°, forexample, with the perpendicular to the silicon surface.

In accordance with at least one embodiment of the method, one methodstep involves depositing a light-emitting diode structure onto the layersequence, that is to say that, for example, the following sequencearises in the growth direction: silicon surface, layer sequence,light-emitting diode structure. The light-emitting diode structure isbased on gallium nitride, for example. The layer sequence serves, forexample, to enable growth of the light-emitting diode structure withrelatively high layer thicknesses of at least 3 μm, for example, atleast 5 μm, and a high material quality on the silicon surface.

In accordance with at least one embodiment of the method, the layersequence contains a GaN layer formed with gallium nitride. By way ofexample, the GaN layer consists of an n-doped gallium nitride.

In this embodiment, the layer sequence furthermore contains a maskinglayer formed with silicon nitride and, for example, consisting ofsilicon nitride. The growth of the masking layer can take place, forexample, by the simultaneous introduction of a silicon precursor suchas, for example, silane or disilane or an organic silicon compoundcomprising a nitrogen precursor such as ammonia or dimethylhydrazineinto the growth chamber in which the epitaxial growth, for example, iseffected. On the growth surface, the two precursors then react to formsilicon nitride.

In this case, the masking layer can be embodied and produced asspecified in the document WO 2007/096405 and U.S. equivalent patentpublication 2007/0197004. With regard to the embodiment and productionof the masking layer described therein, the document WO 2007/096405 ishereby expressly incorporated by reference.

In this case, the masking layer succeeds at least part of the GaN layerin the growth direction. That is to say that, in accordance with thisembodiment of the method, the masking layer is deposited after the firstgrowth of a GaN layer in the growth direction. In this case, the maskinglayer can directly adjoin a GaN layer. In this case, “at least part ofthe GaN layer” means that the masking layer can also be arranged in theGaN layer. That is to say that part of the GaN layer is deposited, thenfollowed by the masking layer and then followed by the rest of the GaNlayer.

In this case, it has been found that applying the masking layer at theearliest after the deposition of a first GaN layer is advantageous forimproving the material quality of a subsequent light-emitting diodestructure. By contrast, introducing a masking layer before thedeposition of a first GaN layer appears to suppress the build-up of acompressive strain in the layer sequence, which leads to an impairmentof the material quality of the light-emitting diode structure.

Overall, a method with late introduction of the masking layer in thelayer sequence, enables a light-emitting diode structure to besubsequently applied to the layer sequence and to have particularly highmaterial quality in conjunction with relatively high layer thickness.The improvement in the material quality in the light-emitting diodestructure can be explained, for example, by the fact that the build-upof a compressive strain in the layer sequence is positively influencedby the late introduction of the masking layer in the layer sequence.

In accordance with at least one embodiment of the method, the maskinglayer is arranged within a GaN layer. In other words, the masking layerin this embodiment directly adjoins a GaN layer both in the growthdirection and counter to the growth direction. The GaN layer is thenpreferably the last GaN layer in the growth direction that is depositedbefore the growth of the light-emitting diode structure.

In accordance with at least one embodiment of the method, at least twoGaN layers are arranged upstream of the masking layer in the growthdirection. That is to say that the masking layer is deposited, forexample, in the third GaN layer of the layer stack. This proves to beadvantageous since the masking layer in this way is deposited relativelylate in the layer stack and thus cannot adversely influence the build-upof a compressive strain.

In accordance with at least one embodiment of the method, the maskinglayer is an incompletely closed layer. Windows are then formed in themasking layer, in which windows the GaN layer adjoined by the maskinglayer on both sides is not perforated by the masking layer.

In accordance with at least one embodiment of the method, the layersequence contains at least two GaN layers. Each of the GaN layers issucceeded by an AlN layer and/or an AlGaN layer in the growth direction.This is the case in particular also for the last GaN layer in the growthdirection in the layer stack, such that the light-emitting diodestructure can, for example, directly succeed the last AlN layer or thelast AlGaN layer in the layer stack.

If an AlGaN layer is used, then it preferably has a small Ga proportionof between, for example, at least 5% and at most 10%.

In accordance with at least one embodiment of the method, the layersequence contains at least two GaN layers and a masking layer isarranged within each GaN layer of the at least two GaN layers. By way ofexample, a masking layer can then be arranged within each GaN layer ofthe layer sequence.

The masking layer is a masking layer as described further above. Themasking layer within the GaN layer therefore adjoins a GaN (partial)layer in each case in the growth direction and counter to the growthdirection. The introduction of a masking layer into at least two or intoeach GaN layer of the layer sequence influences the build-up of acompressive strain in the layer sequence particularly positively.

In accordance with at least one embodiment of the method, the layersequence between the silicon surface and the first succeeding maskinglayer as seen in the growth direction of the layer sequence from thesilicon surface is free of an AlGaN layer. In other words, the layersequence contains no AlGaN transition layer at least in the regionbefore the occurrence of the first masking layer.

Contrary to the view represented in the document U.S. Pat. No. 6,617,060B1, for example, it has been found that an AlGaN transition layer can bedispensed with at least in places in the layer stack. The AlGaN layer isprovided, in particular, for reducing the strains which arise as aresult of the different coefficients of thermal expansion between thecarrier substrate, in particular the silicon surface, and the grown GaNlayers and which build up during the cooling of the layer sequence. Itis to be expected, however, that many further matching dislocations formas a result of the effective contraction of the GaN layers relative tothe silicon surface during the cooling of the layer sequence. Therefore,dispensing with the AlGaN layer can prove to be advantageous.

In accordance with at least one embodiment, the layer sequence overallis free of an AlGaN layer. That is to say that, in this embodiment, noAlGaN transition layer is arranged in the entire layer sequence.

In accordance with at least one embodiment of the method, a GaN layerdirectly succeeds the buffer layer, arranged on the silicon surface, inthe growth direction, wherein the GaN layer is, in particular, apseudomorphic GaN layer. The pseudomorphic GaN layer is distinguished,inter alia, by the fact that it realizes an inverse strain with respectto the underlying layers. During the cooling of the layer sequence, thepseudomorphic GaN layer can therefore counteract a contraction of theoverlying further GaN layers relative to the silicon surface.

In this case, a pseudomorphic GaN layer is understood to be, inparticular, a GaN layer grown with maintenance of the crystal structureof the silicon surface. In this case, it is also possible, inparticular, for the lattice constant of the silicon surface to betransferred to the pseudomorphic GaN layer.

In accordance with at least one embodiment of the method, in the growthdirection a first masking layer is arranged between the pseudomorphicGaN layer and a further GaN layer. The masking layer can, for example,directly adjoin the two GaN layers, that is to say that it is arrangedwithin a GaN layer, wherein that part of the GaN layer which lies belowthe masking layer in the growth direction is pseudomorphic and that partof the GaN layer which lies above the masking layer in the growthdirection is non-pseudomorphic.

In this case, it has been found that introducing a pseudomorphic GaNlayer in conjunction with an advantageously embodied masking layer,which is preferably an SiN masking layer, has the effect that thesubsequent GaN layer grows anew on the pseudomorphic GaN layer partlycovered by the masking layer and, in this case, dislocations which canoriginate from the underlying layers or arise there can be effectivelyblocked.

Preferably, the masking layer in this case has a thickness of between atleast 0.5 nm and at most 2.5 nm, in particular in the range of betweenat least 1 nm and at most 2 nm. In this case, the masking layer ispreferably embodied as a non-closed layer, as described above. Themasking layer has windows, for example, and covers the underlyingpseudomorphic GaN layer in the manner of a net.

In accordance with at least one embodiment of the method, thelight-emitting diode structure is detached from the layer sequence afterits application. The light-emitting diode structure can then be used,for example, in the form of a substrateless diode. Furthermore, it ispossible for the light-emitting diode structure to be applied to acarrier by its side remote from the layer sequence, prior to detachment.The carrier can, for example, contain silicon or germanium or consist ofone of the materials.

BRIEF DESCRIPTION OF THE DRAWINGS

The method described here is explained in greater detail below on thebasis of exemplary embodiments and the associated figures.

FIGS. 1 and 6 show graphical plots on the basis of which the methoddescribed here is elucidated in greater detail; and

FIGS. 2, 3, 4 and 5 show schematic sectional illustrations ofepitaxially produced layer structures on the basis of which the methoddescribed here is elucidated in greater detail.

Elements that are identical, of identical type or act identically areprovided with the same reference symbols in the figures. The figures andthe size relationships of the elements illustrated in the figures amongone another should not be regarded as to scale. Rather, individualelements may be illustrated with an exaggerated size in order to enablebetter illustration and/or in order to afford better understanding.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 shows a graphical plot of the curvature K of the layers depositedonto the silicon surface of the layer sequence and also of thelight-emitting diode structure against the growth time T in seconds. Inthis case, the growth direction R corresponds to the temporal profile.FIG. 1 illustrates two curves. Curve A relates to an exemplaryembodiment in which a masking layer formed with silicon nitride is grownbefore the first GaN layer of the layer sequence 100.

The schematic sectional illustration in FIG. 2 shows one such layerprofile. The carrier substrate 1 with its silicon surface la issucceeded by the masking layer 12, which is succeeded by the first GaNlayer 5 of the layer stack 100 in the growth direction R. The layerstack 100 comprises with the GaN layers 5, 8 and 11 a total of three GaNlayers.

Curve B relates to an exemplary embodiment in which the masking layer isarranged in the third GaN layer 11 of the layer stack 100. This iselucidated graphically on the basis of a schematic sectionalillustration, for example, in FIG. 3.

As is evident from FIG. 1, the curvature in case B is greater than forcase A particularly in the region of the light-emitting diode structure16. Temporally later introduction of the masking layer 12 into the layersequence 100 therefore leads to a greater compressive strain of thegrown layers.

The sequence of the layers is here, for example, for case B as follows(see the schematic sectional illustration in FIG. 3).

The layer structure 100 comprises a carrier substrate 1, which consistsof silicon, for example, and has a silicon surface, for example, a (111)surface 1 a.

The following layers of the layer sequence 100 are deposited onto thesilicon surface one on top of another in the growth direction R, forexample directly:

-   -   a nucleation layer 2 composed of aluminum nitride,    -   a buffer layer 3 composed of aluminum nitride, which is        deposited at higher growth temperatures, for example, at least        1000° C., than the nucleation layer 2,    -   an AlGaN layer 4, in which the aluminum concentration decreases        in a gradated manner from at most 95% to at least 15% in the        growth direction R,    -   a first GaN layer 5,    -   an AlN layer or AlGaN layer 7, which can be grown at lower        growth temperatures of approximately 850° C.,    -   a second GaN layer 8,    -   a subsequent AlN layer or AlGaN layer 10, which can in turn be        grown at approximately 850° C.,    -   a third GaN layer 11, within which the masking layer 12 is        arranged, and    -   an AlN layer or AlGaN layer 15.

The light-emitting diode structure 16 is arranged at that side of theAlN layer or AlGaN layer 15 which is remote from the carrier substrate1, the light-emitting diode structure comprising, for example, multiplequantum well structures and being based on GaN.

The layer structure corresponding to curve A is illustrated in FIG. 2.

A further exemplary embodiment of a method described here is explainedin greater detail in conjunction with FIG. 4. The sequence of layersillustrated schematically in the sectional illustration in FIG. 4 isproduced by means of the method.

In contrast to the sequence of layers as described in conjunction withFIG. 3, the layer sequence 100 in this exemplary embodiment comprises amasking layer 12 between each GaN layer 5, 8, 11, the masking layer 12being formed with silicon nitride and, for example, consisting ofsilicon nitride. In this case, the masking layers 12 can have in eachcase a thickness of at least 0.35 nm and at most 0.65 nm as measured inthe growth direction R.

The introduction of a masking layer 12 into each GaN layer of the layersequence 100 leads, at that surface of the layer sequence 100 which isremote from the carrier substrate 1, to the build-up of a particularlyhigh compressive strain, which allows a light-emitting diode structure16 to be grown which has a thickness of up to 8 μm as measured in thegrowth direction R, without cracks occurring in the light-emitting diodestructure 16.

A further exemplary embodiment of a method described here is explainedin greater detail in conjunction with FIG. 5. In contrast to theexemplary embodiment in FIG. 2, for example, the layer sequence 100 inthe present case is free of an AlGaN transition layer. The layerconstruction of the layer sequence 100 in the growth direction can be asfollows, for example:

-   -   a substrate 1 having a silicon surface 1 a,    -   a nucleation layer 2 and a buffer layer 3, which can in each        case consist of aluminum nitride, for example, and have a        thickness together of approximately 200 nm,    -   a GaN layer 5 a, which is grown in pseudomorphic fashion and has        a thickness of approximately 100 nm,    -   a first masking layer 12, which is formed with silicon nitride,        for example, and has a thickness of between 1 nm and 2 nm,    -   a further GaN layer 8, which has a thickness of approximately        700 nm,    -   a first AlN layer 10, which can be grown for example at a        temperature of approximately 850° C.,    -   a third GaN layer 11, which has a thickness of approximately 700        nm, for example, and    -   a further AlN layer 15, which can be grown at low growth        temperatures of approximately 850° C.

This layer sequence 100 is succeeded by the light-emitting diodestructure 16, having a thickness of between 4 μm and 8 μm, for example.

The exemplary embodiment in FIG. 5 is distinguished, in particular, bythe fact than an AlGaN transition layer between the buffer layer 3 andthe first masking layer 12 is dispensed with.

The effect of dispensing with the AlGaN transition layer 4 isillustrated graphically in conjunction with FIG. 6. In this respect,FIG. 6 shows the full width at half maximum values of the x-ray rockingcurves for different reflections.

The values A in FIG. 6 relate to a reference structure, as shown in FIG.2, for example, which contains an AlGaN layer 4. The values B relate toa layer sequence 100, as illustrated in FIG. 5, in which the transitionlayer AlGaN is dispensed with.

In particular, FIG. 6 shows lower values for the full width at halfmaximum values of the x-ray rocking curves for the reflections 102 and201. This is a clear indication of a reduced defect density of edgedislocations. This allows the expectation of a higher internal quantumefficiency in an active layer of the light-emitting diode structure 16,the active layer being designed for generating radiation. In addition,such a layer sequence 100 can be produced significantly more simply andthus more cost-effectively.

In FIGS. 2, 3 and 4 and also in the description concerning FIG. 5,exemplary thicknesses or thickness ranges are indicated for each layer.In this case, the thicknesses or the indicated limits for the ranges ofthicknesses can fluctuate in ranges of +/−30%, preferably +/−20%,particularly preferably +/−10%, around the indicated values.

The invention is not restricted to the exemplary embodiments by thedescription on the basis of the exemplary embodiments. Rather, theinvention encompasses any novel feature and also any combination offeatures, which in particular includes any combination of features inthe patent claims, even if this feature or this combination itself isnot explicitly specified in the patent claims or exemplary embodiments.

What is claimed is:
 1. A method for producing a layer structure, themethod comprising: providing a carrier substrate having a siliconsurface; and depositing a layer sequence on the silicon surface in agrowth direction; wherein the layer sequence contains a GaN layer formedwith gallium nitride, wherein the layer sequence contains a firstmasking layer formed with silicon nitride, wherein the first maskinglayer succeeds at least part of the GaN layer in the growth direction,and wherein the first masking layer is deposited after depositing anyGaN layer in the layer sequence and the layer sequence is free of anymasking layer in between the GaN layer and the silicon surface.
 2. Themethod according to claim 1, wherein the first masking layer is arrangedwithin the GaN layer.
 3. The method according to claim 1, wherein thefirst masking layer directly adjoins two GaN layers.
 4. The methodaccording to claim 1, wherein at least two GaN layers are arrangedbefore the first masking layer in the growth direction.
 5. The methodaccording to claim 1, wherein the layer sequence contains at least twoGaN layers, and each GaN layer is succeeded by an AlN layer in thegrowth direction.
 6. The method according to claim 1, wherein the layersequence contains at least two GaN layers, and each GaN layer issucceeded by an AlGaN layer in the growth direction.
 7. The methodaccording to claim 1, wherein the layer sequence contains at least twoGaN layers, and each GaN layer is succeeded by an AlGaN layer and/or anAlN layer in the growth direction.
 8. The method according to claim 7,wherein a Ga concentration in at least one of the AlGaN layers is atleast 5% and at most 10%.
 9. The method according to claim 1, whereinthe layer sequence contains at least two GaN layers, and a masking layeris arranged within each GaN layer.
 10. The method according to claim 1,wherein the layer sequence between the silicon surface and the firstmasking layer in the growth direction is free of an AlGaN layer.
 11. Themethod according to claim 1, wherein the layer sequence is free of anAlGaN layer.
 12. The method according to claim 1, further comprisingforming a buffer layer over the carrier substrate, wherein a GaN layerdirectly succeeds the buffer layer in the growth direction.
 13. Themethod according to claim 12, wherein the GaN layer that directlysucceeds the buffer layer in the growth direction is a pseudomorphic GaNlayer.
 14. The method according to claim 13, wherein the first maskinglayer in the growth direction is arranged between the pseudomorphic GaNlayer and a further GaN layer, wherein the first masking layer has athickness between 0.5 nm and 2.5 nm.
 15. The method according to claim1, further comprising depositing an active structure onto the layersequence.
 16. The method according to claim 15, wherein the activestructure is detached from the layer sequence.
 17. The method accordingto claim 1, wherein the first masking layer is grown after depositingthe GaN layer.
 18. The method according to claim 1, wherein forming thelayer sequence comprises: depositing a nucleation layer composed ofaluminum nitride directly onto the silicon surface, and depositing abuffer layer composed of aluminum nitride directly onto the nucleationlayer, the buffer layer deposited at a higher growth temperature thanthe nucleation layer; and depositing a pseudomorphic GaN layer directlyonto the buffer layer.
 19. A method for producing a layer structure, themethod comprising: providing a carrier substrate having a siliconsurface; and depositing a layer sequence on the silicon surface in agrowth direction; wherein the layer sequence contains a GaN layer formedwith gallium nitride; wherein the layer sequence contains a firstmasking layer formed with silicon nitride; wherein the first maskinglayer succeeds at least part of the GaN layer in the growth direction;wherein the first masking layer is grown after depositing the GaN layer;wherein the GaN layer directly succeeds a buffer layer in the growthdirection; and wherein the GaN layer is a pseudomorphic GaN layer. 20.The method according to claim 19, wherein depositing the layer sequencecomprises: depositing a nucleation layer composed of aluminum nitridedirectly onto the silicon surface, and depositing a buffer layercomposed of aluminum nitride directly onto the nucleation layer, thebuffer layer deposited at a higher growth temperature than thenucleation layer; and depositing the pseudomorphic GaN layer directlyonto the buffer layer.
 21. A method for producing a layer structure, themethod comprising: providing a carrier substrate having a siliconsurface; and depositing a layer sequence on the silicon surface in agrowth direction; wherein the layer sequence contains a GaN layer formedwith gallium nitride; wherein the layer sequence contains a firstmasking layer formed with silicon nitride; wherein the first maskinglayer succeeds at least part of the GaN layer in the growth direction;and wherein forming the layer sequence comprises: directly depositing anucleation layer composed of aluminum nitride onto the silicon surface,and directly depositing a buffer layer composed of aluminum nitride ontothe nucleation layer, the buffer layer deposited at a higher growthtemperature than the nucleation layer; and directly depositing apseudomorphic GaN layer onto the buffer layer.